Pt. II: Oxygen Isotopes in Meteorites. Stefan Schröder February 14, 2006 Lecture Series “Origin of Solar Systems” by Dr. Klaus Jockers. Outline. Short summary on meteorite types Introduction, definitions Three-isotope correlation diagram Terrestrial Fractionation line
February 14, 2006
“Origin of Solar Systems”
by Dr. Klaus Jockers
Chondritescontain chondrules, spherules of once molten silicates, and white lumps, called refractory inclusions (the earliest solid matter), in a matrix. Chondrite parent bodies have not undergone large scale melting, homogenization, and differentiation, and thus retain signatures of their early history
Achondrites have been melted (and in some cases homogenized, and differentiated), so that their pre-accretional internal isotopic variations are (usually) not preserved
System to classify meteorites using oxygen isotopes is largely the work of Robert Clayton et al.
Isotopic fractionation can occur through (examples):
Any process that leads to a change in δ17O will produce a change twice as large in δ18O, since the mass difference is twice as large → slope ½.
Spinel is the most refractory: represents the composition of the primary nebula
Clayton (1993)Allende’s calcium-aluminum-rich inclusions (CAI) define the Carbonaceous Chondrite Anhydrous Mineral line
Chondrules of enstatite (MgSiO3) chondrites (× E) on TF line;
Chondrules of carbonaceous chondrites (○ C) border CCAM (CAI) line
Suggests enstatite chondrite material as building block for Earth (Javoy et al. 1986)
In carbonaceous chondrites (Mighei-type) high-temperature anhydrous silicates (e.g. olivine) co-exist with low-temperature phyllosilicates (clay minerals).
The latter are predominant in the matrix, and are thought to have been formed from the former by interaction at low temperature (0°C) with water, enriched in heavier isotopes.